US11035327B2 - Engine device - Google Patents

Abstract

An engine device including: an EGR device configured to circulate, as EGR gas, a portion of exhaust gas exhausted from an exhaust manifold manifold to an intake manifold; and an EGR cooler configured to cool EGR gas and supply the EGR gas to the EGR device. The EGR cooler includes a heat exchanger and a pair of flange portions. The heat exchanger has a coolant passage and an EGR gas fluid passage alternately stacked. The flange portions are disposed on the heat exchanger. An outlet of the coolant is disposed in one of the flange portions, while an inlet of the coolant is disposed in the other flange portion. An inlet of the EGR gas is disposed in one of the flange portions, while an outlet of the EGR gas is disposed in the other flange portion.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 16/088,796 filed Sep. 26, 2018, which is a national stage application pursuant to 35 U.S.C. § 371 of International Application No. PCT/JP2017/010037 filed Mar. 13, 2017, which claims priority under 35 U.S.C. § 119 to Japanese Application No. 2016-066823 filed Mar. 29, 2016, and Japanese Application No. 2016-066824 filed Mar. 29, 2016, the disclosures of which are hereby incorporated by reference in their entireties.

DESCRIPTIONTechnical Field

The present invention relates to an engine device configured to partially circulate exhaust gas to an intake side as EGR gas.

Background

Traditionally, as a countermeasure against exhaust gas of diesel engines and the like, there has been a technology that adopts an EGR device (exhaust-gas recirculation device), which circulates a portion of exhaust gas to an intake side, to keep the combustion temperature low, thereby reducing an amount of NOx (nitrogen oxide) in the exhaust gas.

Examples of such a type of EGR device are disclosed inPatent Literature 1 to Patent Literature 4 (hereinafter referred to asPTL 1 toPTL 4, respectively) and the like. In each of the EGR devices as described inPTL 1 toPTL 3, a recirculation flow pipe passage branched off from an exhaust manifold of a diesel engine is connected to an intake manifold. By supplying a portion of the exhaust gas (EGR gas) to the intake manifold through the recirculation flow pipe passage, the EGR gas is mixed with fresh air from the intake side, the mixed gas is introduced into cylinders (cylinders in an air intake step) of the diesel engine.

An installation space for a diesel engine varies depending on a work vehicle (such as a construction machine or an agricultural machine) to which the diesel engine is installed. Recently, due to demand for weight reduction and compactification, the installation space is often restricted (confined). It therefore is necessary that component parts of the diesel engine are arranged in a compact layout. In addition to such a problem of the restricted installation space, a structure with a high rigidity is required of a cylinder head because component parts such as an EGR device and a turbocharger are coupled to and supported by the cylinder head.

Further, when an EGR cooler (EGR heat exchanger) and an oil cooler (oil heat exchanger) are integrally structured as inPTL 1, it is necessary to seal oil and cooling water which are liquids and EGR gas which is a gas. Due to differences in the characteristics of these fluids, a sealing structure will become complicated. When the cylinder head is connected, thermal deformation in the cylinder head may influence the connection status. Therefore, integrating the EGR cooler with the oil cooler to form a large device limits the connecting portion to the cylinder head, consequently causing an increase in the size of the engine device. On the other hand, a structure in which cooling water flows to an EGR valve device as inPTL 2 will not only lead to a complicated structure of the EGR valve device itself but also necessitate connection of a cooling water pipe and an EGR gas pipe.

If the EGR cooler is connected through a pipe, the volume of the EGR gas increases due to an increase in the temperature of the EGR gas caused by generated heat of the diesel engine. Due to this, a sufficient amount of the EGR gas is cannot be maintained, and reduction of the NOx in the exhaust gas becomes difficult. On the other hand, if the EGR gas is excessively cooled by having the EGR pipe exposed to cooling air from a cooling fan and the like, the combustion in the cylinder is affected. For the reasons above, appropriate arrangement and structure of parts in the diesel engine and an appropriate cooling structure need to be considered for the purpose of supplying the EGR gas at an appropriate temperature. To add this, if there is unevenness in the mixture distribution of the EGR gas and fresh air, the amounts of EGR gas in the fresh air supplied to a plurality of cylinders will be uneven. This affects actions of reducing the NOx and combustion in each of the cylinders, thus deteriorating the operation efficiency of the diesel engine.

A technical problem of the present invention is to provide an engine device that is improved based on studies on the existing circumstances as mentioned above.

CITATION LIST

PTL 1: Japanese Patent No. 3852255

PTL 2: Japanese Patent No. 4071370

PTL 3: Japanese Patent No. 4484800

PTL 4: Japanese Patent Application Laid-Open No. 2000-008969

SUMMARY OF INVENTION

An aspect of the present invention is an engine device including: an exhaust manifold disposed on one of left and right sides of a cylinder head and an intake manifold disposed on the other one of left and right sides of the cylinder head; an EGR device configured to circulate, as EGR gas, a portion of exhaust gas exhausted from the exhaust manifold to the intake manifold; and an EGR cooler configured to cool the EGR gas and supply the EGR gas to the EGR device. In the engine device: the EGR cooler includes a heat exchanger in which coolant passages and EGR gas fluid passages are alternately stacked and a pair of left and right flange portions provided respectively at right and left end portions of one side surface of the heat exchanger; an inlet of a coolant is disposed in one of the left and right flange portions and an outlet of the coolant is disposed in the other of the left and right flange portions; an inlet of EGR gas is disposed in one of the left and right flange portions and an outlet of the EGR gas is disposed in the other of the left and right flange portions; and the left and right flange portions are connected to one of front and rear sides of the cylinder head.

The above engine device may be such that: a space is formed between the heat exchanger in the EGR cooler and the cylinder head.

The above engine device may be such that: the inlet of the coolant and the outlet of the EGR gas are provided to one of the left and right flange portions, and the outlet of the coolant and the inlet of the EGR gas are provided to the other one of the left and right flange portions; the inlet of the coolant and the outlet of the EGR gas are disposed one above the other in the flange portion, and the outlet of the coolant and the inlet of the EGR gas are disposed one above the other in the flange portion; and the inlet of the coolant and the inlet of the EGR gas are disposed at the same height, and the outlet of the coolant and the outlet of the EGR gas are disposed at the same height.

The above engine device may be such that the cylinder head includes: an upstream EGR passage communicating a side surface where the exhaust manifold is disposed to a side surface where the EGR cooler is disposed; a downstream EGR passage communicating a side surface where the intake manifold is disposed to a side surface where the EGR cooler is disposed; an upstream coolant passage communicating the inlet of the coolant; and a downstream coolant passage communicating the outlet of the coolant, the downstream coolant passage being provided nearby the upstream EGR passage, the upstream coolant passage being provided nearby the downstream EGR passage.

The above engine device may be such that a plate-shape gasket is interposed between the cylinder head and the flange portions in such a manner as to extend across the left and right flange portions, a ring-shape seal member is embedded in each of the outlet and the inlet of the coolant in the cylinder head respectively communicating with the inlet and the outlet of the coolant in the flange portions, and the seal member is surrounded by the flange portions.

The above engine device may be such that the EGR device includes a main body case configured to mix the fresh air with the EGR gas and supply the mixed gas to the intake manifold, the main body case being configured so that a fresh air flow direction and an EGR gas flow direction therein cross each other perpendicularly or with an obtuse angle, and that a direction in which a mixed gas of the EGR gas and the fresh air is taken into the intake manifold intersects each of the fresh air flow direction and the EGR gas flow direction.

The above engine device may be such that a fresh air inlet to which fresh air is supplied is opened in one of the front and rear sides of the main body case, whereas an EGR gas inlet to which the EGR gas is supplied is opened in the other of the front and rear sides of the main body case; an intake outlet communicating with the intake manifold is opened on one of the left and right sides of the main body case, the intake outlet and the EGR gas inlet are disposed at the same height, and the fresh air inlet and the EGR gas inlet are disposed at different heights.

The above engine device may be such that the main body case includes a first case with the fresh air inlet and a second case with the intake outlet and the EGR gas inlet coupled with each other.

The above engine device may be such that the first case is provided therein with a first EGR gas fluid passage constituting a part of the EGR gas passage where the EGR gas flows and a mixing chamber in which fresh air and the EGR gas are mixed; and the second case is provided with a second EGR gas fluid passage through which the first EGR gas fluid passage is in communication with the EGR gas inlet and a mixed gas fluid passage through which mixed gas obtained by mixing the fresh air with the EGR gas is supplied from the mixing chamber to the intake manifold.

The above engine device may be such that the first EGR gas fluid passage is coupled with an offset to a side surface of the mixing chamber opposite to a side surface thereof having the intake outlet relative to a central axis of the mixing chamber, and the first EGR gas fluid passage and the second EGR gas fluid passage are in communication with each other so that the EGR gas fluid passage is formed in a spiral manner.

With the above aspect of the present invention, since each of the pair of left and right flange portions has a coolant opening and an EGR gas opening, it is possible that the flange portions are made from a common member, and moreover material costs of the flange portions can be suppressed. In addition, a coupling portion where the flange portions are coupled to the heat exchanger can be minimized, so that the amount of heat transfer from the cylinder head to the heat exchanger can be reduced, which increases the effect of cooling the EGR gas by the heat exchanger.

In the above aspect of the present invention, a space is formed between the heat exchanger and the cylinder head. As a result, the EGR cooler is in a state where a wide area of the front and rear surfaces of the heat exchanger is exposed to outside air. Heat dissipation occurs in the heat exchanger, too. Thus, the effect of cooling the EGR gas by the EGR cooler is increased. This configuration can reduce the volume of the heat exchanger as compared to a configuration in which the entire surface of the heat exchanger is attached. Thus, the engine device can be downsized.

In the above aspect of the present invention, the coolant outlet and the EGR gas inlet are disposed one above the other in one of the flange portions, while the EGR gas outlet and the coolant outlet are disposed one above the other in the other of the flange portions. Thus, the flange portions having identical shapes with their postures mutually upside-down are attached to the heat exchanger. This can reduce the number of types of component parts included in the EGR cooler, thus improving an assemblability of the EGR cooler and reducing costs of the component parts.

In the EGR cooler of the above aspect of the present invention, the coolant outlet and the coolant inlet are disposed at diagonal positions, and the EGR gas inlet and the EGR gas outlet are disposed at diagonal positions. Since EGR gases having different quantities of heat and coolants having different quantities of heat are respectively supplied or discharged at diagonal positions, thermal deformations of coupling portions where the EGR cooler is coupled to the cylinder head can be mutually relieved, so that deflection or slackness of the coupling portions can be suppressed. Accordingly, leakage of an EGR gas or a coolant in the EGR cooler and in the cylinder head can be prevented, and moreover a decrease in the coupling strength can be prevented.

In the above aspect of the present invention, the EGR gas is sealed by the gasket and the coolant is sealed by an O-ring, thereby improving the sealability. This way, even though the EGR cooler where a liquid and a gas enter and exit is coupled to the cylinder head, a sealability for each of the liquid and the gas can be obtained, so that leakage of each of the EGR gas and the coolant can be prevented.

In the main body case of the EGR device in the above aspect of the present invention, the EGR gas flow direction is at an angle of 90° or more relative to the fresh air flow direction, and the fresh air flow and the EGR gas flow intersect each other, so that a distribution of mixture of the EGR gas with the fresh air can be made uniform, and an uneven flow of the EGR gas in the intake manifold can be suppressed. As a result, a concentration of the EGR gas in the mixed gas supplied from the intake manifold to each of the plurality of intake fluid passages can be made uniform. Thus, a variation in combustion action among cylinders of the engine device can be suppressed, and the EGR device can be compactly configured.

In the above aspect of the present invention, the fresh air taken into the fresh air inlet flows in the front-rear direction and then in the up-down direction while curving in an L-shape, whereas the EGR gas taken into the EGR gas inlet flows obliquely upward and mixed in the mixing chamber. Therefore, the EGR gas flows in toward a flow of the fresh air, which facilitates mixing of the EGR gas with the fresh air. The mixed gas of the fresh air and the EGR gas flows in the up-down direction and then in the left-right direction while curving in an L-shape, to flow into the intake manifold through the intake outlet. A direction in which the mixed gas is emitted intersects not only the directions in which the fresh air and the EGR gas are taken in but also the directions in which the fresh air and the EGR gas flow within the main body case. Consequently, a distribution of mixture of the EGR gas with the fresh air can be made uniformed.

With the above aspect of the present invention, since the main body case is divisible into the first case and the second case, a mixed fluid passage where the EGR gas flow and the fresh air flow intersect each other at an angle of 90° or more can be easily formed in the main body case. It therefore is possible that the main body case is formed as a casting with a high rigidity, and moreover, weight reduction of the collector can be obtained by forming the collector as an aluminum-based casting product. Furthermore, each of the EGR gas fluid passage, the mixing chamber, and the mixed gas fluid passage can be compactly configured within the main body case, and thus the main body case can be downsized.

In the above aspect of the present invention, the EGR gas inlet is disposed in the second case while the fresh air inlet and the mixing chamber are disposed in the first case. In the mixing chamber, therefore, the fresh air flowing from the fresh air inlet and the EGR gas flowing from the second case intersect each other, so that the fresh air and the EGR gas can be efficiently mixed. In addition, the intake outlet is disposed in the second case, and the fresh air having entered the first case tends to flow toward the second case. As a result, mixing of the EGR gas flowing toward the first case with the fresh air is made uniform.

In the above aspect of the present invention, a portion of the mixing chamber that is in communication with the EGR gas fluid passage is on the side opposite to the intake outlet. The EGR gas flowing into the mixing chamber, therefore, reaches the intake outlet while being guided by a fresh air flow, which allows the EGR gas to be uniformly mixed with the fresh air. The EGR gas flowing from the EGR gas fluid passage into the mixing chamber flows in a direction against the direction from the mixing chamber toward the mixed gas fluid passage. This causes the fresh air and the EGR gas to collide with each other while flowing within the mixing chamber. Accordingly, the EGR gas is smoothly mixed with the fresh air.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a front view of an engine.

FIG. 2 illustrates a rear view of the engine.

FIG. 3 illustrates a left side view of the engine.

FIG. 4 illustrates a right side view of the engine.

FIG. 5 illustrates a top plan view of the engine.

FIG. 6 illustrates a bottom plan view of the engine.

FIG. 7 illustrates a perspective view of the engine as viewed from diagonally front.

FIG. 8 illustrates a perspective view of the engine as viewed from diagonally rear.

FIG. 9 illustrates an enlarged perspective view of a cylinder head as viewed from an intake manifold side.

FIG. 10 illustrates an exploded perspective view of the cylinder head as viewed from an exhaust manifold side.

FIG. 11 illustrates an exploded perspective view of the cylinder head as viewed from the intake manifold side.

FIG. 12 illustrates a top plan view of the cylinder head.

FIG. 13 illustrates a front view of the cylinder head.

FIG. 14 illustrates a perspective cross-sectional view of the cylinder head and an EGR device.

FIG. 15 illustrates a perspective cross-sectional view of the cylinder head and the exhaust manifold.

FIG. 16 illustrates a perspective cross-sectional view of a coupling portion of the cylinder head coupled to an EGR cooler.

FIG. 17 illustrates a perspective cross-sectional view of the EGR device.

FIG. 18 illustrates a top plan view of the EGR device.

FIG. 19 illustrates an exploded perspective view of the EGR device.

FIG. 20 illustrates an exploded view of a collector in the EGR device.

FIG. 21 illustrates an exploded view of a collector in the EGR device.

FIG. 22 illustrates an exploded view of the coupling portion of the cylinder head coupled to the EGR cooler.

FIG. 23 illustrates a rear view of the EGR cooler.

FIG. 24 illustrates a cross-sectional view of the coupling portion of the cylinder head coupled to the EGR cooler.

DESCRIPTION OF EMBODIMENTS

In the following, an embodiment of the present invention will be described with reference to the drawings. First, referring toFIG. 1 toFIG. 8, an overall structure of a diesel engine (engine device)1 will be described. In the descriptions below, opposite side portions parallel to a crankshaft5 (side portions on opposite sides relative to the crankshaft5) will be defined as left and right, a side where aflywheel housing7 is disposed will be defined as front, and a side where a coolingfan9 is disposed will be defined as rear. For convenience, these are used as a benchmark for a positional relationship of left, right, front, rear, up, and down in thediesel engine1.

As shown inFIG. 1 toFIG. 8, anintake manifold3 and anexhaust manifold4 are disposed in one side portion and the other side portion of thediesel engine1 parallel to thecrankshaft5. In the embodiment, theintake manifold3 provided on a right surface of acylinder head2 is formed integrally with thecylinder head2. Theexhaust manifold4 is provided on a left surface of thecylinder head2. Thecylinder head2 is mounted on acylinder block6 in which thecrankshaft5 and a piston (not shown) are disposed.

Thecrankshaft5 has its front and rear distal ends protruding from front and rear surfaces of thecylinder block6. Theflywheel housing7 is fixed to one side portion of the diesel engine1 (in the embodiment, a front surface side of the cylinder block6) intersecting thecrankshaft5. A flywheel8 is disposed in theflywheel housing7. The flywheel8, which is pivotally supported on the front end side of thecrankshaft5, is configured to rotate integrally with thecrankshaft5. The flywheel8 is configured such that power of thediesel engine1 is extracted to an actuating part of a work machine (for example, a hydraulic shovel, a forklift, or the like) through the flywheel8. The coolingfan9 is disposed in the other side portion of the diesel engine1 (in the embodiment, a rear surface side of the cylinder block6) intersecting thecrankshaft5. A rotational force is transmitted from the rear end side of thecrankshaft5 to the coolingfan9 through a V-belt10.

Anoil pan11 is disposed on a lower surface of thecylinder block6. A lubricant is stored in theoil pan11. The lubricant in theoil pan11 is suctioned by an oil pump (not shown) disposed on the right surface side of thecylinder block6, the oil pump being arranged in a coupling portion where thecylinder block6 is coupled to theflywheel housing7. The lubricant is then supplied to lubrication parts of thediesel engine1 through anoil cooler13 and anoil filter14 that are disposed on the right surface of thecylinder block6. The lubricant supplied to the lubrication parts is then returned to theoil pan11. The oil pump (not shown) is configured to be driven by rotation of thecrankshaft5.

In the coupling portion where thecylinder block6 is coupled to theflywheel housing7, afuel feed pump15 for feeding a fuel is attached. Thefuel feed pump15 is disposed below anEGR device24. Acommon rail16 is fixed to a side surface of thecylinder block6 at a location below theintake manifold3 of thecylinder head2. Thecommon rail16 is disposed above thefuel feed pump15. Injectors (not shown) for four cylinders are provided on an upper surface of thecylinder head2 which is covered with ahead cover18. Each of the injectors has a fuel injection valve of electromagnetic-controlled type.

Each of the injectors is connected to a fuel tank (not shown) through thefuel feed pump15 and thecommon rail16 having a cylindrical shape. The fuel tank is mounted in a work vehicle. A fuel in the fuel tank is pressure-fed from thefuel feed pump15 to thecommon rail16, so that a high-pressure fuel is stored in thecommon rail16. By controlling the opening/closing of the fuel injection valves of the injectors, the high-pressure fuel in thecommon rail16 is injected from the injectors to the respective cylinders of thediesel engine1.

A blow-bygas recirculation device19 is provided on an upper surface of thehead cover18 covering intake and exhaust valves (not shown), etc. disposed on the upper surface of thecylinder head2. The blow-bygas recirculation device19 takes in a blow-by gas that has leaked out of a combustion chamber of thediesel engine1 or the like toward the upper surface of thecylinder head2. A blow-by gas outlet of the blow-bygas recirculation device19 is in communication with an intake part of a two-stage turbocharger30 through arecirculation hose68. A blow-by gas, from which a lubricant component is removed in the blow-bygas recirculation device19, is then recirculated to theintake manifold3 via the two-stage turbocharger30.

Anengine starting starter20 is attached to theflywheel housing7. Theengine starting starter20 is disposed below theexhaust manifold4. A position where theengine starting starter20 is attached to theflywheel housing7 is below a coupling portion where thecylinder block6 is coupled to theflywheel housing7.

Acoolant pump21 for smoothing a coolant is provided in a portion of the rear surface of thecylinder block6, the portion being a little left-hand. Thecoolant pump21 is disposed below the coolingfan9. Rotation of thecrankshaft5 causes thecoolant pump21 as well as the coolingfan9 to be driven through the cooling fan driving V-belt10. Driving thecoolant pump21 causes a coolant in a radiator (not shown) mounted in the work vehicle to be supplied to thecoolant pump21. The coolant is then supplied to thecylinder head2 and thecylinder block6, to cool thediesel engine1.

Thecoolant pump21 is disposed below theexhaust manifold4, and acoolant inlet pipe22 is provided on the left surface of thecylinder block6 and is fixed at a height equal to the height of thecoolant pump21. Thecoolant inlet pipe22 is in communication with a coolant outlet of the radiator. Acoolant outlet pipe23 that is in communication with a coolant inlet of the radiator is fixed to an upper rear portion of thecylinder head2. Thecylinder head2 has acoolant drainage35 that protrudes rearward from theintake manifold3. Thecoolant outlet pipe23 is provided on an upper surface of thecoolant drainage35.

The inlet side of theintake manifold3 is coupled to an air cleaner (not shown) via a collector (EGR main body case)25 of an EGR device24 (exhaust-gas recirculation device) which will be described later. Fresh air (outside air) suctioned by the air cleaner is subjected to dust removal and purification in the air cleaner, then fed to theintake manifold3 through thecollector25, and then supplied to the respective cylinders of thediesel engine1. In the embodiment, thecollector25 of theEGR device24 is coupled to the right side of theintake manifold3 which is formed integrally with thecylinder head2 to form the right surface of thecylinder head2. That is, an outlet opening of thecollector25 of theEGR device24 is coupled to an inlet opening of theintake manifold3 provided on the right surface of thecylinder head2. In this embodiment, thecollector25 of theEGR device24 is coupled to the air cleaner via an intercooler (not shown) and the two-stage turbocharger30, as will be described later.

TheEGR device24 includes: thecollector25 serving as a relay pipe passage that mixes a recirculation exhaust gas of the diesel engine1 (an EGR gas from the exhaust manifold4) with fresh air (outside air from the air cleaner), and supplies a mixed gas to theintake manifold3; anintake throttle member26 that communicates thecollector25 with the air cleaner; a recirculationexhaust gas tube28 that constitutes a part of a recirculation flow pipe passage connected to theexhaust manifold4 via anEGR cooler27; and anEGR valve member29 that communicates thecollector25 with the recirculationexhaust gas tube28.

TheEGR device24 is disposed on the right lateral side of theintake manifold3 in thecylinder head2. TheEGR device24 is fixed to the right surface of thecylinder head2, and is in communication with theintake manifold3 in thecylinder head2. In theEGR device24, thecollector25 is coupled to theintake manifold3 on the right surface of thecylinder head2, and an EGR gas inlet of the recirculationexhaust gas tube28 is coupled and fixed to a front portion of theintake manifold3 on the right surface of thecylinder head2. TheEGR valve member29 and theintake throttle member26 are coupled to the front and rear of thecollector25, respectively. An EGR gas outlet of the recirculationexhaust gas tube28 is coupled to the rear end of theEGR valve member29.

TheEGR cooler27 is fixed to the front surface of thecylinder head2. The coolant and the EGR gas flowing in thecylinder head2 flows into and out of theEGR cooler27. In theEGR cooler27, the EGR gas is cooled. EGRcooler coupling bases33,34 for coupling theEGR cooler27 to the front surface of thecylinder head2 protrude from left and right portions of the front surface of thecylinder head2. TheEGR cooler27 is coupled to the coupling bases33,34. That is, theEGR cooler27 is disposed on the front side of thecylinder head2 and at a position above theflywheel housing7 such that a rear end surface of theEGR cooler27 and the front surface of thecylinder head2 are spaced from each other.

The two-stage turbocharger30 is disposed on a lateral side (in the embodiment, the left lateral side) of theexhaust manifold4. The two-stage turbocharger30 includes a high-pressure turbocharger51 and a low-pressure turbocharger52. The high-pressure turbocharger51 includes a high-pressure turbine53 in which a turbine wheel (not shown) is provided and a high-pressure compressor54 in which a blower wheel (not shown) is provided. The low-pressure turbocharger52 includes a low-pressure turbine55 in which a turbine wheel (not shown) is provided and a low-pressure compressor56 in which a blower wheel (not shown) is provided.

Anexhaust gas inlet57 of the high-pressure turbine53 is coupled to theexhaust manifold4. Anexhaust gas inlet60 of the low-pressure turbine55 is coupled to anexhaust gas outlet58 of the high-pressure turbine53 via a high-pressureexhaust gas tube59. An exhaust gas introduction side end portion of an exhaust gas discharge pipe (not shown) is coupled to anexhaust gas outlet61 of the low-pressure turbine55. A fresh air supply side (fresh air outlet side) of the air cleaner (not shown) is connected to a fresh air inlet port (fresh air inlet)63 of the low-pressure compressor56 via anair supply pipe62. A freshair inlet port66 of the high-pressure compressor54 is coupled to a fresh air supply port (fresh air outlet)64 of the low-pressure compressor56 via a low-pressure freshair passage pipe65. A fresh air introduction side of the intercooler (not shown) is connected to a freshair supply port67 of the high-pressure compressor54 via a high-pressure fresh air passage pipe (not shown).

The high-pressure turbocharger51 is coupled to theexhaust gas outlet58 of theexhaust manifold4, and is fixed to the left lateral side of theexhaust manifold4. On the other hand, the low-pressure turbocharger52 is coupled to the high-pressure turbocharger51 via the high-pressureexhaust gas tube59 and the low-pressure freshair passage pipe65, and is fixed above theexhaust manifold4. Thus, theexhaust manifold4 and the high-pressure turbocharger51 with a small diameter are disposed side-by-side with respect to the left-right direction below the low-pressure turbocharger52 with a large diameter. As a result, the two-stage turbocharger30 is arranged so as to surround the left surface and the upper surface of theexhaust manifold4. That is, theexhaust manifold4 and the two-stage turbocharger30 are arranged so as to form a rectangular shape in a rear view (or front view), and are compactly fixed to the left surface of thecylinder head2.

Next, referring toFIG. 9 toFIG. 16, a configuration of thecylinder head2 will be described. As shown inFIG. 9 toFIG. 16, thecylinder head2 is provided with a plurality ofintake fluid passages36 for taking fresh air into a plurality of intake ports (not shown) and a plurality ofexhaust fluid passages37 for emitting an exhaust gas from a plurality of exhaust ports. Theintake manifold3 which aggregates the plurality ofintake fluid passages36 is formed integrally with a right side portion of thecylinder head2. Since thecylinder head2 is integrated with theintake manifold3, a gas sealability between theintake manifold3 and theintake fluid passages36 can be enhanced, and in addition, the rigidity of thecylinder head2 can be increased.

Thecylinder head2 is configured such that theexhaust manifold4 is coupled to the left surface of thecylinder head2 which is opposite to the right surface where theintake manifold3 is provided, and theEGR cooler27 is coupled to the front surface (a surface on theflywheel housing7 side) of thecylinder head2 which is adjacent to the left and right surfaces. Coupling bases (EGR cooler coupling bases)33,34 to which theEGR cooler27 is coupled are provided so as to protrude from the front surface of thecylinder head2. The coupling bases33,34 are provided therein with EGR gas fluid passages (EGR gas relay fluid passages)31,32 and coolant passages (coolant relay fluid passages)38,39.

Since the EGR gasrelay fluid passages31,32 and thecoolant passages38,39 are provided in the coupling bases33,34 to which theEGR cooler27 is coupled, it is not necessary that coolant piping and EGR gas piping are disposed between theEGR cooler27 and thecylinder head2. This can give a sealability to a coupling portion coupled to theEGR cooler27 without any influence of, for example, extension and contraction of piping caused by the EGR gas or the coolant. This can also enhance a resistance (structural stability) against external fluctuation factors such as heat and vibration, and moreover can make the configuration compact.

Thecylinder head2 includes an upstream EGR gasrelay fluid passage31 through which a front portion of the left surface is in communication with the front surface. AnEGR gas outlet41 disposed at the front end of theexhaust manifold4 is in communication with the upstream EGR gasrelay fluid passage31. Thecylinder head2 also includes a downstream EGR gasrelay fluid passage32 through which a front portion of the right surface (on the front side of the intake manifold3) is in communication with the front surface. The EGR gas inlet of the recirculationexhaust gas tube28 is in communication with the downstream EGR gasrelay fluid passage32. Thecylinder head2 has the EGRcooler coupling bases33,34 which are formed by left and right edges of the front surface of the cylinder head2 (a front-left corner portion and a front-right corner portion of the cylinder head2) being protruded frontward. The upstream EGR gasrelay fluid passage31 is provided inside thecoupling base33, and the downstream EGR gasrelay fluid passage32 is provided inside thecoupling base34.

TheEGR device24 is coupled to theintake manifold3 which is provided on the right surface of thecylinder head2 so as to protrude therefrom. Theintake manifold3 is disposed in a portion of the right surface of thecylinder head2, the portion being relatively close to the rear side (the coolingfan9 side). Theintake manifold3 is formed by a lower portion of the right surface of thecylinder head2 being protruded rightward. Theintake manifold3 has anintake inlet40 at its middle portion with respect to the front-rear direction. Anintake outlet83 of thecollector25 of theEGR device24 is coupled to theintake inlet40 of theintake manifold3 which protrudes from the right surface of thecylinder head2, and theEGR device24 is fixed to the right lateral side of thecylinder head2.

On the front side (theflywheel housing7 side) of the right surface of thecylinder head2, thecoupling base34 coupled to theEGR cooler27 protrudes frontward, and an EGR gas outlet of the downstream EGR gasrelay fluid passage32 is opened in a right surface of thecoupling base34. One end of the recirculationexhaust gas tube28 of theEGR device24 is coupled to the right surface of thecoupling base34, and thereby thecollector25 of theEGR device24 is in communication with the downstream EGR gasrelay fluid passage32 provided inside thecylinder head2 via the recirculationexhaust gas tube28 and theEGR valve member29.

On the rear side (the coolingfan9 side) of the right surface of thecylinder head2, the coolant drainage (thermostat case)35 whose upper surface is opened to communicate with a coolant outlet pipe (thermostat cover)23 protrudes rearward, and a thermostat (not shown) is installed therein. Thecoolant drainage35 is offset at the rear of the right surface of thecylinder head2, and therefore it is possible that the V-belt10 wound on a fan pulley9ato which the coolingfan9 is fixed extends through a space below thecoolant drainage35. Thus, the length of thediesel engine1 in the front-rear direction can be shortened. Thecoolant drainage35 also protrudes from the right surface of thecylinder head2. On the right surface of thecylinder head2, theintake manifold3 and thecoolant drainage35 are arranged one behind the other with respect to the front-rear direction.

On the front side (theflywheel housing7 side) of the left surface of thecylinder head2, thecoupling base33 coupled to theEGR cooler27 protrudes frontward, and an EGR gas inlet of the upstream EGR gasrelay fluid passage31 is opened in a left surface of thecoupling base33. That is, in the left surface of thecylinder head2, the EGR gas inlet of the upstream EGR gasrelay fluid passage31 and exhaust gas outlets of the plurality ofexhaust fluid passages37 are disposed in the front-rear direction, and are opened. Theexhaust manifold4 has, in its right surface which is coupled to the left surface of thecylinder head2, theEGR gas outlet41 which is in communication with the upstream EGR gasrelay fluid passage31 andexhaust gas inlets42 which are in communication with the plurality ofexhaust fluid passages37 are arranged in the front-rear direction, and are opened. Since the EGR inlet and the exhaust gas outlets are disposed side-by-side in the same surface of thecylinder head2, it is easy for a coupling portion where thecylinder head2 is coupled to theexhaust manifold4 to obtain an airtightness (gas sealability) by sandwiching asingle gasket45 therebetween.

Theexhaust manifold4 is provided therein with anexhaust aggregate part43 which is in communication with theEGR gas outlet41 and theexhaust gas inlets42. The exhaustaggregate part43 is disposed such that its longitudinal direction is parallel to the front-rear direction. Anexhaust gas outlet44 which is in communication with the exhaustaggregate part43 is opened in a rear portion of the left surface of theexhaust manifold4. Theexhaust manifold4 is configured such that, after an exhaust gas coming from theexhaust fluid passages37 of thecylinder head2 flows into the exhaustaggregate part43 via theexhaust gas inlets42, part of the exhaust gas serves as an EGR gas and flows into the upstream EGR gasrelay fluid passage31 of thecylinder head2 via theEGR gas outlet41 while the rest of the exhaust gas flows into the two-stage turbocharger30 via theexhaust gas outlet44.

On the front surface of thecylinder head2, the left and right pair of EGRcooler coupling bases33,34 are disposed on theexhaust manifold4 side and on theintake manifold3 side, respectively. The EGRcooler coupling base33 has the upstream EGR gasrelay fluid passage31 through which the EGR gas fluid passage of theexhaust manifold4 communicates with the EGR gas fluid passage of theEGR cooler27. The EGRcooler coupling base34 has the downstream EGR gasrelay fluid passage32 through which the EGR gas fluid passage of theEGR device24 communicates with the EGR gas fluid passage of theEGR cooler27. The EGRcooler coupling base33 also has thedownstream coolant passage38 to which a coolant is discharged from theEGR cooler27. The EGRcooler coupling base34 has theupstream coolant passage39 that supplies a coolant to theEGR device24 and to theEGR cooler27.

Since the EGRcooler coupling bases33,34 are configured in a protruding manner, there is no need for EGR gas piping that communicates theexhaust manifold4, theEGR cooler27, and theEGR device24. Thus, the number of coupling portions of the EGR gas fluid passage is small. Accordingly, in thediesel engine1 that aims to reduce NOx by the EGR gas, EGR gas leakage can be reduced, and moreover deformation can be suppressed which may otherwise be caused by a change in a stress due to extension and contraction of piping. Since the EGR gasrelay fluid passages31,32 and thecoolant passages38,39 are provided in the EGRcooler coupling bases33,34, the shapes of thefluid passages31,32,38,39 formed in thecylinder head2 are simplified, so that thecylinder head2 can be easily formed by casting without using a complicated core.

The EGRcooler coupling base33 on theintake manifold3 side and the EGRcooler coupling base34 on theexhaust manifold4 side are distant from each other. This can suppress a mutual influence between thermal deformations of the coupling bases33,34. Accordingly, gas leakage and damage of coupling portions where the EGRcooler coupling bases33,34 are coupled to theEGR cooler27 can be prevented, and in addition, a balance of the rigidity of thecylinder head2 can be maintained. Moreover, the volume of the front surface of thecylinder head2 can be reduced, which leads to weight reduction of thecylinder head2. Furthermore, it is possible that theEGR cooler27 is disposed at a distance from the front surface of thecylinder head2, to provide a space on the front and rear sides of theEGR cooler27. This enables cool air to flow around theEGR cooler27, thus increasing the cooling efficiency of theEGR cooler27.

In the EGRcooler coupling base33, thedownstream coolant passage38 is disposed above the upstream EGR gasrelay fluid passage31. In the EGRcooler coupling base34, the downstream EGR gasrelay fluid passage32 is disposed above theupstream coolant passage39. A coolant inlet of thedownstream coolant passage38 and an EGR gas inlet of the downstream EGR gasrelay fluid passage32 are disposed at the same height. A coolant outlet of theupstream coolant passage39 and an EGR gas outlet of the downstream EGR gasrelay fluid passage32 are disposed at the same height.

Since the EGR gasrelay fluid passages31,32 and thecoolant passages38,39 are provided in the EGRcooler coupling bases33,34 protruding at a distance from each other, a mutual influence between thermal deformations of the EGRcooler coupling bases33,34 is relieved. In the EGRcooler coupling bases33,34, the EGR gas flowing in the EGR gasrelay fluid passages31,32 is cooled by the coolant flowing in thecoolant passages38,39, so that thermal deformations of the EGRcooler coupling bases33,34 are suppressed. In addition, the up-down positional relationship of the EGR gasrelay fluid passages31,32 and thecoolant passages38,39 in one of the EGRcooler coupling bases33,34 is reverse to that in the other of the EGRcooler coupling bases33,34. As a result, heat distributions in the respective EGRcooler coupling bases33,34 are in opposite directions with respect to the up-down direction, which can reduce an influence of thermal deformation in the height direction in thecylinder head2.

An outer peripheral wall of thecylinder head2 stands upward at a peripheral edge of the upper surface of thecylinder head2, to provide aspacer46 which is coupled to a peripheral edge of a lower surface of thehead cover18. Thespacer46 has, in a right surface thereof, a plurality ofopenings47.Fuel pipes48 which couple injectors (not shown) provided in thecylinder head2 to thecommon rail16 pass through theopenings47. Since thespacer46 integrated with thecylinder head2 is disposed above thecylinder head2, the rigidity of thecylinder head2 is increased, which can reduce distortion of thecylinder head2 itself and also can allow component parts coupled to thecylinder head2 to be supported with a high rigidity.

A configuration of theEGR device24 will now be described with reference toFIG. 9 toFIG. 15, andFIG. 17 toFIG. 21. As shown inFIG. 9 toFIG. 15, andFIG. 17 toFIG. 21, theEGR device24 includes the collector (main body case)25 that mixes fresh air with an EGR gas, and supplies a mixture to theintake manifold3. Theintake manifold3 and theintake throttle member26 for taking fresh air in are connected in communication with each other via thecollector25. TheEGR valve member29 which leads to an outlet side of the recirculationexhaust gas tube28 is connected in communication with thecollector25.

In thecollector25, a fresh air flow direction and an EGR gas flow direction cross each other perpendicularly or with an obtuse angle, and a direction in which a mixed gas of the EGR gas and the fresh air is taken into theintake manifold3 intersects each of the fresh air flow direction and the EGR gas flow direction. Afresh air inlet81 to which the fresh air is supplied is opened in one of front and rear surfaces of thecollector25, whereas anEGR gas inlet82 to which the EGR gas is supplied is opened in the other of the front and rear surfaces of thecollector25. Theintake outlet83 which is coupled to theintake manifold3 is opened in a left surface of thecollector25. TheEGR gas inlet82 and theintake outlet83 are disposed at the same height, and thefresh air inlet81 and theEGR gas inlet82 are disposed at different heights.

In thecollector25, fresh air taken from theintake throttle member26 into thefresh air inlet81 flows in the front-rear direction and then in the up-down direction while curving in an L-shape, whereas an EGR gas taken from theEGR valve member29 into theEGR gas inlet82 flows obliquely upward. As a result, the EGR gas flows in toward a flow of the fresh air, which facilitates mixing of the EGR gas with the fresh air. The mixed gas of the fresh air and the EGR gas flows in the up-down direction and then in the left-right direction while curving in an L-shape, to flow into theintake manifold3 through theintake outlet83. A direction in which the mixed gas is emitted intersects not only the directions in which the fresh air and the EGR gas are taken in but also the directions in which the fresh air and the EGR gas flow within thecollector25. Consequently, a distribution of mixture of the EGR gas with the fresh air can be made uniformed.

In thecollector25, as described above, the EGR gas flow direction is at an angle of 90° or more relative to the fresh air flow direction, and the fresh air flow and the EGR gas flow intersect each other, so that a distribution of mixture of the EGR gas with the fresh air can be made uniform, and an uneven flow of the EGR gas in theintake manifold3 can be suppressed. As a result, a concentration of the intake EGR gas supplied to each of the plurality ofintake fluid passages36 of thecylinder head2 can be made uniform. Thus, a variation in combustion action among cylinders of thediesel engine1 can be suppressed. Consequently, generation of black smoke is suppressed, and the amount of NOx can be reduced while a good combustion state of thediesel engine1 is maintained. That is, purifying (cleaning) the exhaust gas by a recirculation flow of the EGR gas can be achieved without causing a misfire in a specific cylinder.

Thecollector25 includes an upper case (first case)84 with thefresh air inlet81 and a lower case (second case)85 with theEGR gas inlet82 and theintake outlet83 being coupled to each other. Since thecollector25 is divisible in the up-down direction into theupper case84 and thelower case85, a mixed fluid passage where the EGR gas flow and the fresh air flow intersect each other at an angle of 90° or more can be easily formed in thecollector25. It therefore is possible that thecollector25 is formed as a casting with a high rigidity, and moreover, weight reduction of thecollector25 can be obtained by forming thecollector25 as an aluminum-based casting product.

Theupper case84 is provided therein with a downstream EGR gas fluid passage (first EGR gas fluid passage)86awhich is a part of the EGRgas fluid passage86 where the EGR gas flows and a mixingchamber87 in which the fresh air and the EGR gas are mixed. Thelower case85 is provided therein with an upstream EGR gas fluid passage (second EGR gas fluid passage)86bthrough which the downstream EGRgas fluid passage86ais in communication with theEGR gas inlet82 and a mixedgas fluid passage88 through which a mixed gas obtained by mixing the fresh air with the EGR gas is supplied from the mixingchamber87 to theintake manifold3.

TheEGR gas inlet82 is disposed in thelower case85 while thefresh air inlet81 and the mixingchamber87 are disposed in theupper case84. In the mixingchamber87, therefore, the fresh air flowing from thefresh air inlet81 and the EGR gas flowing from thelower case85 intersect each other, so that the fresh air and the EGR gas can be efficiently mixed. In addition, theintake outlet83 is disposed in thelower case85, and the fresh air having entered theupper case84 tends to flow toward thelower case85. As a result, mixing of the EGR gas flowing toward theupper case84 with the fresh air is made uniform. Furthermore, each of the EGRgas fluid passage86, the mixingchamber87, and the mixedgas fluid passage88 can be compactly configured within thecollector25, and thus thecollector25 can be downsized.

In a plan view, the downstream EGRgas fluid passage86ais coupled with an offset to a side surface (right side surface) of the mixingchamber87 opposite to a side surface (left side surface) thereof having theintake outlet83 relative to a central axis of the mixingchamber87, and the downstream EGRgas fluid passage86aand the upstream EGRgas fluid passage86bare in communication with each other so that the EGRgas fluid passage86 is formed in a spiral manner. The EGRgas fluid passage86 composed of the downstream EGRgas fluid passage86aand the upstream EGRgas fluid passage86bhas a bent shape curved toward the side (right side) opposite to theintake outlet83 in a plan view. A bottom of the upstream EGRgas fluid passage86bis constituted by a slope (a slope inclined upward toward the rear) extending from theEGR gas inlet82 toward theupper case84.

A portion of the mixingchamber87 that is in communication with the EGRgas fluid passage86 is on the side opposite to theintake outlet83. The EGR gas flowing into the mixingchamber87, therefore, reaches theintake outlet83 while being guided by a fresh air flow, which allows the EGR gas to be uniformly mixed with the fresh air. The EGR gas flowing from the EGRgas fluid passage86 into the mixingchamber87 flows in a direction against the direction from the mixingchamber87 toward the mixedgas fluid passage88. This causes the fresh air and the EGR gas to collide with each other while flowing within the mixingchamber87. Accordingly, the EGR gas is smoothly mixed with the fresh air.

Since the EGR gas flows along the EGRgas fluid passage86 having a spiral shape, the EGR gas creates a swirling flow having a clockwise vortex when flowing into the mixingchamber87. Such a turbulent EGR gas flows in a direction against the fresh air gas flow. Thus, simultaneously with flowing into the mixingchamber87, the EGR gas is smoothly mixed with the fresh air flowing within the mixingchamber87. In thecollector25, therefore, the fresh air and the EGR gas can be efficiently mixed (the EGR gas can be smoothly dispersed in the mixed gas) by agitation before they are fed to theintake manifold3, so that a variation (unevenness) in the gas mixing state within thecollector25 can be suppressed more reliably. As a result, a mixed gas having less unevenness can be distributed to the respective cylinders of thediesel engine1, and a variation in the EGR gas amount among the cylinders can be suppressed. Accordingly, it is possible to suppress generation of black smoke, and to reduce the amount of NOx while maintaining a good combustion state of thediesel engine1. In addition, the EGRgas fluid passage86 having a spiral shape gives sufficient swirling properties to the EGR gas flowing into the mixingchamber87. Thus, thecollector25 can be shaped with a shortened length in the front-rear direction.

Alower surface flange84aof theupper case84 and anupper surface flange85aof thelower case85 are fastened with bolts, to form thecollector25 having openings (thefresh air inlet81, theEGR gas inlet82, and the intake outlet83) in three directions (toward the front, rear, and left). Theupper case84 has arear surface flange84bin which thefresh air inlet81 is opened, and a fresh air outlet of theintake throttle member26 is fastened to therear surface flange84bwith bolts. Theintake throttle member26 adjusts the degree of opening of an intake valve (butterfly valve)26aprovided therein, to thereby adjust the amount of fresh air supply to thecollector25.

Thelower case85 has afront surface flange85bin which theEGR gas inlet82 is opened, and an EGR gas outlet of theEGR valve member29 is fastened with bolts to thefront surface flange85bwith interposition of arelay flange89 having a rectangular pipe shape. TheEGR valve member29 adjusts the degree of opening of an EGR valve (not shown) provided therein, to thereby adjust the amount of EGR gas supply to thecollector25. Areed valve90 inserted in theEGR gas inlet82 is fixed inside thefront surface flange85bof thelower case85. The relay flange (spacer)89 which is fastened to thefront surface flange85bwith bolts covers the front side of thereed valve90. As a result, thecollector25 is provided therein with thereed valve90 disposed in a portion of the EGRgas fluid passage86, the portion being on theEGR gas inlet82 side.

Therelay flange89 has, in its rear surface coupled to thecollector25, anEGR gas outlet89awhich is in communication with theEGR gas inlet82. Therelay flange89 has a front surface from which valve coupling bases89b,89cto be coupled to theEGR valve member29 protrude. Openings of the valve coupling bases89b,89care in communication with the EGR gas outlet of theEGR valve member29. In therelay flange89, the EGR gas is merged at EGR gas inlets of the upper and lower valve coupling bases89b,89c, and then is caused to flow from theEGR gas inlet82 into the EGRgas fluid passage86 provided inside thecollector25 via thereed valve90.

TheEGR valve member29 is configured such that: avalve body29ehas an EGRgas fluid passage29fin which an EGR valve (not shown) is disposed; anactuator29dfor adjusting the degree of opening of the EGR valve is disposed above thevalve body29e; theEGR valve member29 has its longitudinal direction in parallel to the up-down direction; and theEGR valve member29 is coupled to the front side of thecollector25 with interposition of therelay flange89. TheEGR valve member29 has, in a rear surface of thevalve body29ewhich is arranged lower,outlet side flanges29a,29bto be coupled respectively to the valve coupling bases89b,89cof therelay flange89. Theoutlet side flanges29a,29bare arranged one above the other. TheEGR valve member29 also has, in its front surface, aninlet side flange29chaving an EGR gas inlet that is in communication with the EGR gas outlet of the recirculationexhaust gas tube28.

TheEGR valve member29 is configured such that: after an EGR gas cooled by theEGR cooler27 flows into the EGR gas inlet of theinlet side flange29cthrough the downstream EGR gasrelay fluid passage32 of the EGRcooler coupling base34 and the recirculationexhaust gas tube28, the EGR gas is distributed to upper and lower parts via the EGRgas fluid passage29fof thevalve body29e. The EGR gas flow distributed to upper and lower parts through the EGRgas fluid passage29fis then subjected to a flow rate adjustment by the EGR valve, and then enters therelay flange89 through the EGR gas outlets of the upper and loweroutlet side flanges29a,29b.

The recirculationexhaust gas tube28 includes agas pipe portion28aand arib28b, thegas pipe portion28abeing bent to have an L-shape in a plan view, therib28bhaving a flat-plate shape protruding from an inner peripheral side of an outer wall of thegas pipe portion28a. The recirculationexhaust gas tube28 has, at one end (rear end) of thegas pipe portion28a, anoutlet side flange28cto be coupled to theinlet side flange29cof theEGR valve member29, and also has, at the other end (left end) of thegas pipe portion28a, aninlet side flange28dto be coupled to the right surface of the EGRcooler coupling base34. The recirculationexhaust gas tube28 further has, in an upper surface of a bent portion of thegas pipe portion28a, asensor attachment base28eto which an EGR gas temperature sensor is attached.

In theEGR device24, thecollector25 can be configured with a shortened length, and therefore the distance between theEGR valve member29 and theintake throttle member26 can be shortened, which enables the length of theEGR device24 in the front-rear direction to be shortened. In theEGR valve member29, theactuator29dis disposed on the upper side. It therefore is possible that topmost portions of theEGR valve member29, thecollector25, and theintake throttle member26 are at the same height. This can lower the height of theEGR device24 in the up-down direction, and also can narrow the width of theEGR device24 in the left-right direction. Since theEGR device24 can be configured compactly, coupling theEGR device24 to the right side of thecylinder head2 integrated with theintake manifold3 can be easily implemented merely by adjusting the recirculationexhaust gas tube28. In addition, such a configuration contributes to downsizing of thediesel engine1.

The recirculationexhaust gas tube28 has the flat-plate rib28bthat is coupled so as to connect the opposite ends of thegas pipe portion28a. This gives a high rigidity to the recirculationexhaust gas tube28, and also increases a strength with which the front end side of theEGR device24 is supported on thecylinder head2. In addition, the recirculationexhaust gas tube28 has the flat-plate rib28bthat is disposed along an EGRgas fluid passage28fprovided inside thegas pipe portion28a. Due to therib28b, thegas pipe portion28ahas a wide heat dissipation area, which increases the effect of cooling the EGR gas flowing in the EGRgas fluid passage28f. This contributes to cooling a mixed gas prepared in theEGR device24, and exerts an effect that reduction in the amount of NOx generated from the mixed gas can be easily kept in a proper state.

A configuration of theEGR cooler27 will now be described with reference toFIG. 9 toFIG. 16, andFIG. 22 toFIG. 24. As shown inFIG. 9 toFIG. 16, andFIG. 22 toFIG. 24, theEGR cooler27 includes aheat exchanger91 and a pair of left andright flange portions92,93. Theheat exchanger91 has a coolant passage and an EGR gas fluid passage alternately stacked. The pair of left andright flange portions92,93 are disposed in left and right end portions of one side surface of theheat exchanger91. Thecoolant outlet94 is disposed in one of the left andright flange portions92,93, while thecoolant inlet95 is disposed in the other of the left andright flange portions92,93. TheEGR gas inlet96 is disposed in one of the left andright flange portions92,93, while theEGR gas outlet97 is disposed in the other of the left andright flange portions92,93. The left andright flange portions92,93 are coupled to the front surface of thecylinder head2, so that theEGR cooler27 is fixed to thecylinder head2.

Since each of the pair of left andright flange portions92,93 has a coolant opening and an EGR gas opening, it is possible that theflange portions92,93 are made from a common member, and moreover material costs of theflange portions92,93 can be suppressed. Theflange portions92,93 are formed by a flat plate being bored to have throughholes94 to97 corresponding to the coolant and the EGR gas, the flat plate being coupled to thecylinder head2. Thus, forming theflange portions92,93 in theEGR cooler27 is easy. In addition, a coupling portion where theflange portions92,93 are coupled to theheat exchanger91 can be minimized, so that the amount of heat transfer from thecylinder head2 to theheat exchanger91 can be reduced, which increases the effect of cooling the EGR gas by theheat exchanger91.

Since theEGR cooler27 has theflange portions92,93 protruding from the rear surface of theheat exchanger91, a space is formed between theheat exchanger91 and thecylinder head2. As a result, theEGR cooler27 is in a state where a wide area of the front and rear surfaces of theheat exchanger91 is exposed to outside air. Heat dissipation occurs in theheat exchanger91, too. Thus, the effect of cooling the EGR gas by theEGR cooler27 is increased. This configuration can reduce the degree of stacking in theheat exchanger91 as compared to a configuration in which the rear surface and the front surface of theheat exchanger91 are attached. The length of theEGR cooler27 in the front-direction can be shorted, and thus thediesel engine1 can be downsized.

Theleft flange portion92 has thecoolant outlet94 and theEGR gas inlet96, while theright flange portion93 has thecoolant inlet95 and theEGR gas outlet97. In theleft flange portion92, thecoolant outlet94 is disposed above theEGR gas inlet96, while in theright flange portion93, theEGR gas outlet97 is disposed above thecoolant inlet95. Thecoolant outlet94 and theEGR gas outlet97 are disposed at the same height, while thecoolant inlet95 and theEGR gas inlet96 are disposed at the same height.

The left andright flange portions92,93 of theEGR cooler27 are coupled respectively to the EGRcooler coupling bases33,34 protruding from the front surface of thecylinder head2. The upstream EGR gasrelay fluid passage31 and the downstream coolantrelay fluid passage38 of the left EGRcooler coupling base33 are in communication with theEGR gas inlet96 and thecoolant outlet94 of theleft flange portion92, respectively. The downstream EGR gasrelay fluid passage32 and the upstream coolantrelay fluid passage39 of the right EGRcooler coupling base34 are in communication with theEGR gas outlet97 and thecoolant inlet95 of theright flange portion93, respectively.

The EGR gasrelay fluid passages31,32 and thecoolant passages38,39 are provided in the coupling bases33,34 to which theflange portions92,93 of theEGR cooler27 are coupled, and are in communication with the EGR gas inlet andoutlet96,97 and the coolant outlet andinlet94,95 of theflange portions92,93. It is not necessary that coolant piping and EGR gas piping are disposed between theEGR cooler27 and thecylinder head2. Accordingly, a sealability can be given to a coupling portion where theEGR cooler27 and thecylinder head2 are coupled to each other without any influence of, for example, extension and contraction of piping caused by the EGR gas or the coolant. In addition, theEGR cooler27 is given an enhanced resistance against external fluctuation factors such as heat and vibration, and can be compactly installed in thecylinder head2.

Thecoolant outlet94 is disposed above theEGR gas inlet96 in theflange portion92, while theEGR gas outlet97 is disposed above thecoolant inlet95 in theflange portion93. Thus, theflange portions92,93 having identical shapes with their postures mutually upside-down are attached to theheat exchanger91. This can reduce the number of types of component parts included in theEGR cooler27, thus improving an assemblability of theEGR cooler27 and reducing costs of the component parts.

Theflange portion92 is provided with thecoolant outlet94 and theEGR gas inlet96 through which a coolant or an EGR gas having a large quantity of heat passes, while theflange portion93 is provided with thecoolant inlet95 and theEGR gas outlet97 through which a coolant or an EGR gas having a small quantity of heat passes. Accordingly, distortion caused by thermal deformation of each of theflange portions92,93 can be suppressed. In addition, theflange portions92,93 are configured as separate members whose thermal deformation is less influential to each other, and therefore damage and breakdown of theEGR cooler27 can be prevented.

In theEGR cooler27, thecoolant outlet94 and thecoolant inlet95 are disposed at diagonal positions, and theEGR gas inlet96 and theEGR gas outlet97 are disposed at diagonal positions in a rear view. Since EGR gases having different quantities of heat and coolants having different quantities of heat are respectively supplied or discharged at diagonal positions, thermal deformations of coupling portions where theEGR cooler27 is coupled to thecylinder head2 can be mutually relieved, so that deflection or slackness of the coupling portions can be suppressed. Accordingly, leakage of an EGR gas or a coolant in theEGR cooler27 and in thecylinder head2 can be prevented, and moreover a decrease in the coupling strength can be prevented.

A plate-shapedgasket98 is sandwiched between thecylinder head2 and theflange portions92,93 so as to extend across the left andright flange portions92,93. A coolant inlet and a coolant outlet of thecylinder head2, which are respectively in communication with thecoolant outlet94 and thecoolant inlet95 of theflange portions92,93, have O-rings99 embedded therein, the O-rings99 being ring-shape seal members. The O-rings99 are covered with theflange portions92,93.

Since theflange portions92,93 configured as separate members are coupled to the coupling bases33,34 of thecylinder head2 with thegasket98 interposed therebetween, a tension is exerted on thegasket98 due to thermal deformation of the coupling portion coupled to thecylinder head2. This enhances a sealability (hermetic sealing performance) of thegasket98 in a coupling portion of each of theEGR gas inlet96 and theEGR gas outlet97. Thus, leakage of an EGR gas flowing from one to the other between thecylinder head2 and theEGR cooler27 can be prevented. The O-rings99 are embedded in spaces defined by rear end surfaces of theflange portions92,93 and the coolant inlet and the coolant outlet of the coupling bases33,34 of thecylinder head2. When a coolant flows, therefore, the coolant is in contact with the O-rings99 in communication portions where the coupling bases33,34 are in communication with theflange portions92,93. Thus, a sealability (hermetic sealing performance) of the coupling portions of the coolant outlet and inlet can be obtained. Accordingly, even though theEGR cooler27 where a liquid and a gas enter and exit is coupled to thecylinder head2, a sealability for each of the liquid and the gas can be obtained, so that leakage of each of the EGR gas and the coolant can be prevented.

An outer peripheral portion of each of theflange portions92,93 is bored to have throughholes100 for bolt fastening, at outer positions. Specifically, theleft flange portion92 has five throughholes100 disposed in its upper, lower, and left sides, and theright flange portion93 has five throughholes100 disposed in its upper, lower, and right sides. Since theleft flange portion92 has the throughholes100 disposed above thecoolant outlet94, below theEGR gas inlet96, and to the left of a portion between thecoolant outlet94 and theEGR gas inlet96, a sealability of thecoolant outlet94 and theEGR gas inlet96 can be exerted when theleft flange portion92 is fastened to thecoupling base33 of thecylinder head2 with bolts. Likewise, since theright flange portion93 has the throughholes100 disposed below thecoolant inlet95, above theEGR gas outlet97, and to the right of a portion between thecoolant inlet95 and theEGR gas outlet97, a sealability of thecoolant inlet95 and theEGR gas outlet97 can be exerted when theright flange portion93 is fastened to thecoupling base34 of thecylinder head2 with bolts.

Thegasket98 is constituted by a lamination of twoplates98a,98beach having throughholes101 to103. The EGR gas passes through the through holes (EGR gas through holes)101. The coolant passes through the through holes (coolant through holes)102. Fastening bolts are inserted into the through holes (bolt through holes)103. Thegasket98 has such a shape that an inner peripheral edge at the EGR gas throughhole101 is branched so as to be warped in the front-rear direction and is configured such that the open areas of the coolant throughholes102 are larger than the open areas of the coolant outlet andinlet94,95.

In thegasket98, thefront plate98ahas its inner peripheral edge at the EGR gas throughhole101 being warped frontward, while therear plate98bhas its inner peripheral edge at the EGR gas throughhole101 being warped rearward. Thefront plate98aand therear plate98bare bonded by welding, so that the inner peripheral edge at the EGR gas throughhole101 has a Y-shaped cross-section. Since the inner peripheral edge at the EGR gas throughhole101 is warped in the front-rear direction, front and rear surfaces of the inner peripheral edge at the EGR gas throughhole101 can be in tight contact with end surfaces of the coupling bases33,34 and theflange portions92,93. Accordingly, a sufficient airtightness can be obtained.

Thegasket98 is configured such that the openings of the coolant throughholes102 is larger than those of the coolant outlet andinlet94,95. Thus, the O-rings99 are inserted in the coolant throughholes102. Communication portions where the coolant outlet and inlet of theflange portions92,93 are in communication with the coolantrelay fluid passages38,39 of the coupling bases33,34 are hermetically sealed by the O-rings99 fitted in the coolant throughholes102 of thegasket98.

The coupling bases33,34 of thecylinder head2 have the coolant outlet and inlet opened with steps, and thereby the openings of the coolant outlet and inlet are given larger diameters than the fluid passage diameters of the coolantrelay fluid passages38,39 formed inside the coupling bases33,34. The O-rings99 disposed to the coolant outlet and inlet of the coupling bases33,34 are fitted on the outer circumferential sides of the coolantrelay fluid passages38,39. The O-rings99 are inserted in thegasket98, and also fitted in the step portions of the coolant outlet and inlet in the coupling bases33,34. Thereby, the O-rings99 are sandwiched between the coupling bases33,34 and theflange portions92,93. When a coolant passes inside the O-rings99 made of an elastic material, the O-rings99 are deformed to expand outward and come into tight contact with the coupling bases33,34 and theflange portions92,93, thus providing a sealability for the coolant.

The ring-shape O-ring has its inner circumferential portion bulging frontward and rearward. A coolant passing through the inner circumferential portion of the O-ring99 pushes the inner circumferential portion, so that its front and rear edges are deformed to protrude frontward and rearward. This brings the inner circumferential portion of the O-ring99 into tight contact with the coupling bases33,34 and theflange portions92,93. Thus, a sealability for the coolant can be enhanced in the coupling portion where thecylinder head2 is coupled to theEGR cooler27.

The ring-shape O-ring99 whose inner circumferential portion is bulged frontward and rearward is shaped such that its inner circumferential surface has a recessed portion. The inner circumferential surface of the O-ring is warped frontward and rearward so as to have a Y-shaped cross-section. A coolant passing through the inner circumferential portion of the O-ring99 pushes the inner circumferential portion, so that its front and rear edges are further protruded frontward and rearward, to increase the degree of tight contact of the inner circumferential portion of the O-ring99 with the coupling bases33,34 and theflange portions92,93. Accordingly, a sealability for the coolant can be enhanced in the coupling portion where thecylinder head2 is coupled to theEGR cooler27.

The configurations of respective parts of the present invention are not limited to those of the illustrated embodiment, but can be variously changed without departing from the gist of the invention.

REFERENCE SIGNS LIST

• • 1 engine
  • 2 cylinder head
  • 3 intake manifold
  • 4 exhaust manifold
  • 5 crankshaft
  • 6 cylinder block
  • 7 flywheel housing
  • 8 flywheel
  • 9 cooling fan
  • 24 EGR device
  • 25 collector (EGR main body case)
  • 26 intake throttle member
  • 27 EGR cooler
  • 28 recirculation exhaust gas tube
  • 29 EGR valve member
  • 31 upstream EGR gas relay fluid passage
  • 32 downstream EGR gas relay fluid passage
  • 33 EGR cooler
  • 34 EGR cooler
  • 35 coolant drainage
  • 36 intake fluid passage
  • 37 exhaust fluid passage
  • 38 downstream coolant relay fluid passage
  • 39 upstream coolant relay fluid passage
  • 40 intake inlet
  • 91 heat exchanger
  • 92 flange member
  • 93 flange member
  • 94 coolant outlet
  • 95 coolant inlet
  • 96 EGR gas inlet
  • 97 EGR gas outlet
  • 98 gasket
  • 98afront plate
  • 98brear plate
  • 99 O-ring
  • 100 through hole (for bolt fastening)
  • 101 EGR gas through hole
  • 102 coolant through hole
  • 103 bolt through hole

Claims (20)

The invention claimed is:

1. An engine device comprising:

an exhaust gas recirculation (EGR) device configured to circulate, as EGR gas, a portion of exhaust gas, exhausted from an exhaust manifold, to an intake manifold; and

an EGR cooler configured to cool the EGR gas and supply the EGR gas to the EGR device; and

wherein:

the EGR cooler includes a heat exchanger in which coolant passages and EGR gas fluid passages are disposed, and a plurality of flanges are provided on the heat exchanger;

a first flange of the plurality of flanges is provided with two out of:

an inlet of a coolant;

an outlet of a coolant;

an inlet of the EGR gas; and

an outlet of the EGR gas; and

a second flange of the plurality of flanges is provided with the remaining two of the inlet of the coolant, the outlet of the coolant, the inlet of the EGR gas, and the outlet of the EGR gas.

2. The engine device according toclaim 1, wherein:

the inlet of the coolant and the outlet of the EGR gas are provided on the first flange;

the outlet of the coolant and the inlet of the EGR gas are provided on the second flange;

the inlet of the coolant and the outlet of the EGR gas are disposed one above the other in the first flange, the outlet of the coolant and the inlet of the EGR gas are disposed one above the other in the second flange; and

the inlet of the coolant and the inlet of the EGR gas are disposed at a same height, and the outlet of the coolant and the outlet of the EGR gas are disposed at a same height.

3. The engine device according toclaim 1, wherein:

a space is formed between the heat exchanger in the EGR cooler and a cylinder head.

4. The engine device according toclaim 1, wherein:

the plurality of flanges are connected to one of a front side and a rear side of a cylinder head; and

the cylinder head includes:

an upstream EGR passage configured to be in fluid communication with:

the exhaust manifold disposed on a first side surface of the cylinder head; and

the EGR cooler disposed on a second side surface of the cylinder head;

a downstream EGR passage configured to be in fluid communication with:

the intake manifold disposed on a third side surface of the cylinder head; and

the EGR cooler disposed on the second side surface of the cylinder head;

an upstream coolant passage configured to communicate with the inlet of the coolant; and

a downstream coolant passage configured to communicate with the outlet of the coolant, the downstream coolant passage provided nearby the upstream EGR passage, and the upstream coolant passage provided nearby the downstream EGR passage.

5. The engine device according toclaim 1, wherein:

a plate-shape gasket is interposed between a cylinder head and the plurality of flanges in such a manner as to extend across the first and second flanges;

a ring-shape seal member is embedded in each of the outlet and the inlet of the coolant in the cylinder head respectively communicating with the inlet and the outlet of the coolant in the plurality of flanges; and

the ring-shape seal member is surrounded by the plurality of flanges.

6. The engine device according toclaim 1, wherein:

the EGR device includes a main body case configured to mix fresh air with the EGR gas and supply the mixed gas to the intake manifold; and

the main body case is configured such that a fresh air flow direction and an EGR gas flow direction therein cross each other perpendicularly or with an obtuse angle such that the fresh air flow direction and the EGR gas flow direction intersect each other prior to being received by the intake manifold.

7. The engine device according toclaim 6, wherein:

a fresh air inlet to which the fresh air is supplied is opened in one of a front side or rear side of the main body case;

an EGR gas inlet to which the EGR gas is supplied is opened in the other one of the front side or rear sides of the main body case;

an intake outlet communicating with the intake manifold is opened on one of a left side or right side of the main body case;

the intake outlet and the EGR gas inlet are disposed at a same height; and

the fresh air inlet and the EGR gas inlet are disposed at different heights.

8. The engine device according toclaim 7, wherein:

the main body case includes a first case with the fresh air inlet and a second case with the intake outlet; and

the EGR gas inlet, the first case, and the second case are coupled together.

9. The engine device according toclaim 8, wherein:

the first case includes a first EGR gas fluid passage where the EGR gas flows and a mixing chamber in which the fresh air and the EGR gas are mixed; and

the second case includes a second EGR gas fluid passage through which the first EGR gas fluid passage is in fluid communication with the EGR gas inlet and a mixed gas fluid passage through which the mixed gas obtained by mixing the fresh air with the EGR gas is supplied from the mixing chamber to the intake manifold.

10. The engine device according toclaim 9, wherein:

the first EGR gas fluid passage is coupled with an offset to a first side surface of the mixing chamber, the first side surface opposite a second side surface, the second side surface having the intake outlet relative to a central axis of the mixing chamber; and

the first EGR gas fluid passage and the second EGR gas fluid passage are in fluid communication with each other such that a combination of the EGR gas fluid passages is formed in a spiral manner.

11. An apparatus comprising:an exhaust gas recirculation (EGR) cooler including:

a flange body comprising:

a first side and a second side opposite the first side;

a coolant inlet and a coolant outlet; and

an EGR gas inlet and an EGR gas outlet; and

a heat exchanger positioned such that a first side of the heat exchanger is interposed between the flange body and a second side of the heat exchanger, the second side opposite the first side,

where:

the one of the coolant inlet and the coolant outlet and one of the EGR gas inlet and the EGR gas outlet is disposed on a first portion of the flange body, the first portion being closer to the first side than the second side; and

the other of the coolant inlet and the coolant outlet and the other of the EGR gas inlet and the EGR gas outlet is disposed on a second portion of the flange body, the second portion being closer to the second side than the first side.

12. The apparatus according toclaim 11, wherein:

the flange body is in contact with the heat exchanger; and

the EGR cooler is configured to:

receive an EGR gas via a first flow path from an exhaust manifold to the EGR cooler; and

provide the EGR gas to an intake manifold via a second flow path, the second flow path from the EGR cooler, through an EGR device, and to the intake manifold.

13. The apparatus according toclaim 11, wherein:

the flange body is unitary with the heat exchanger;

the heat exchanger is configured to receive and discharge a coolant; and

the heat exchanger comprises:

a first portion that defines a first passage configured to communicate the coolant; and

a second portion that defines a second passage configured to communicate EGR gas.

14. The apparatus according toclaim 11, wherein:

the flange body includes a first flange and a second flange;

the heat exchanger includes a third side and a fourth side opposite the third side;

the third side and the fourth side of the heat exchanger are interposed between the first side and the second side of the heat exchanger; and

the first flange is positioned on the first portion of the flange body adjacent to the third side of the heat exchanger and the second flange is positioned on the second portion of the flange body adjacent to the fourth side of the heat exchanger.

15. The apparatus according toclaim 14, wherein:

one of the first flange or the second flange comprises the coolant inlet, and the other of the first flange or the second flange comprises the coolant outlet; and

one of the first flange or the second flange comprises the EGR gas inlet, and the other of the first flange or the second flange comprises the EGR gas outlet.

16. The apparatus according toclaim 11, further comprising:

a cylinder head interposed between an intake manifold and an exhaust manifold; and

wherein:

the intake manifold is disposed on a first side of the cylinder head;

the exhaust manifold is disposed on a second side of the cylinder head;

the EGR cooler is disposed on a third side of a cylinder head, the third side different from the first side and the second side; and

the EGR cooler and the cylinder head define a space interposed between the cylinder head and the EGR cooler.

17. An engine device comprising:

an exhaust gas recirculation (EGR) device configured to circulate, as EGR gas, a portion of exhaust gas, exhausted from an exhaust manifold, to an intake manifold, the EGR device includes a main body case configured to mix fresh air with the EGR gas and supply the mixed gas to the intake manifold, the main body case is configured such that a fresh air flow direction and an EGR gas flow direction therein cross each other perpendicularly or with an obtuse angle such that the fresh air flow direction and the EGR gas flow direction intersect each other prior to being received by the intake manifold; and

an EGR cooler configured to cool the EGR gas and supply the EGR gas to the EGR device; and

wherein:

the EGR cooler includes a heat exchanger in which coolant passages and EGR gas fluid passages are disposed, and a flange portion provided on the heat exchanger;

an inlet and an outlet of a coolant are disposed in the flange portion; and

an inlet and an outlet of the EGR gas are disposed in the flange portion.

18. The engine device ofclaim 17, comprising wherein:

the flange portion is connected to one of a front side and a rear side of a cylinder head; and

the cylinder head includes:

an upstream EGR passage configured to be in fluid communication with:

the exhaust manifold disposed on a first side surface of the cylinder head; and

the EGR cooler disposed on a second side surface of the cylinder head;

a downstream EGR passage configured to be in fluid communication with:

the intake manifold disposed on a third side surface of the cylinder head; and

the EGR cooler disposed on the second side surface of the cylinder head;

an upstream coolant passage configured to communicate with the inlet of the coolant; and

a downstream coolant passage configured to communicate with the outlet of the coolant, the downstream coolant passage provided nearby the upstream EGR passage, and the upstream coolant passage provided nearby the downstream EGR passage.

19. The engine device ofclaim 17, wherein:

the flange portion includes a pair of left and right flange portions;

a plate-shape gasket is interposed between a cylinder head and the flange portions in such a manner as to extend across the left and right flange portions;

a ring-shape seal member is embedded in each of the outlet and the inlet of the coolant in the cylinder head respectively communicating with the inlet and the outlet of the coolant in the flange portions; and

the ring-shape seal member is surrounded by the flange portions.

20. The engine device ofclaim 17, further comprising:

a cylinder head interposed between an intake manifold and an exhaust manifold; and

wherein:

the intake manifold is disposed on a first side of the cylinder head;

the exhaust manifold is disposed on a second side of the cylinder head;

the EGR cooler is disposed on a third side of a cylinder head, the third side different from the first side and the second side; and

the EGR cooler and the cylinder head define a space interposed between the cylinder head and the EGR cooler.

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